1. Field of the Invention
The present invention relates to data storage apparatus for magnetically reading and writing information on data storage media. More particularly, the invention concerns suspensions designed to carry read/write heads in magnetic disk drive storage devices.
2. Description of the Prior Art
By way of background, a read/write transducer in a magnetic disk drive storage device (“disk drive”) is typically incorporated on an air bearing slider that is designed to fly closely above the surface of a spinning magnetic disk medium during drive operation. The slider is mounted to the free end of a suspension that in turn is cantilevered from the arm of a rotary actuator mounted on a stationary pivot shaft. The suspension typically has a mount plate end that attaches to the actuator arm, a bend-compliant hinge connected to the mount plate, and a load beam that extends from the hinge to the free end of the suspension where the transducer-carrying slider is mounted on a flexure that allows it to gimbal. The actuator is driven by a rotary voice coil motor that, when energized, causes the actuator to rotate and thereby sweep the actuator arm and its attached suspension across the disk surface. By controlling the rotational movement of the actuator via the voice coil motor, the read/write transducer can be selectively positioned over the surface of the magnetic disk medium, allowing it to read and write data in a series of concentric tracks.
Recent years have seen an increase in TPI (Tracks Per Inch) recording density requirements in order to meet the demand for increased data storage capacity. This has necessitated finer track positioning resolution than is possible using voice coil motor control alone. One solution to the foregoing problem has been to mount a pair of small piezoelectric transducer (PZT) actuators to the suspension. The PZT actuators are usually oriented in a spaced parallel arrangement, but angled configurations have also been proposed. When energized, the PZT actuators impart small sway (i.e., across-track) displacements to the suspension. Each sway displacement causes the read/write head mounted at the free end of the suspension to move several tracks in either direction from its nominal position, depending on the polarity of the energy that drives the PZT actuators.
FIG. 1 is illustrative. It shows a suspension S that has two PZT actuators A1 and A2. The actuators A1 and A2 are spaced from each other by a distance of 2*r, where “r” is the distance from the displaceable end of each actuator (the other end being relatively statically fixed) to a pivot point “P” about which the suspension pivots due to PZT actuation. A distance “R” exists between a read/write transducer T and the pivot point P. When the displaceable ends of the actuators are respectively displaced by a positive and negative stroke length of magnitude “d” (i.e., one actuator is lengthened while the other is shortened), a sway stroke offset “D” will be produced at the read/write transducer T.
The PZT actuators thus provide a second stage of suspension actuation that enhances the primary actuation provided by the voice coil motor. For this reason, suspensions having PZT actuators may be referred to as “dual stage” (or “two stage”) suspensions. Very fine track positioning resolution can be obtained with a dual stage suspension. Moreover, because the response time of the secondary stage PZT actuators is generally much less than that of the primary stage voice coil motor, the seek and settle latency associated with data storage and retrieval operations can be reduced in situations where the read/write head only needs to move a few (e.g., 1-4) tracks at a time.
The above-described PZT actuators are sometimes referred to as “microactuators.” However, the term “milliactuator” is perhaps more appropriate in order to distinguish such elements from another type of PZT (or electrostatic) actuator that is mounted directly under, or near, the slider. This latter type of actuator, known as a “microactuator,” has smaller movement (e.g., 1-2 tracks) than the “milliactuator” elements described above. However, due to their location under or near the slider, microactuators have better dynamic characteristics than milliactuators, which are located near the suspension hinge. The present invention concerns PZT actuators of the milliactuator type that are mounted in proximity to the suspension hinge.
Current disk drive suspensions tend to be about 11-18 mm in length. With the trend toward ever increasing data densities, future designs will see suspension lengths of 11 mm or less. This presents a problem relative to prior art milliactuator systems. Because a disk drive suspension is normally swage-mounted to its associated actuator arm, it usually has a relatively large swage spud at its mount plate end to be connected to a swage hole in the actuator arm. In order to maintain adequate clearance with respect to the swage spud while providing the required sway stroke, PZT actuators are typically spaced longitudinally from the swage spud and mounted on an elongated portion of the suspension mount plate. It will be appreciated that accommodating the actuators in this fashion is contrary to the goal of reducing suspension length. Although some manufacturers have proposed artificial shortening of the suspension's functional end (e.g., load beam) as a solution to this problem, this approach impacts other suspension properties such as dynamic characteristics.
Accordingly, a need exists for a suspension design that facilitates the effective use of PZT actuators to increase track positioning resolution in disk drive suspensions of reduced length. Preferably, this design will not increase the mass and inertia of the suspension and will avoid introducing undesirable dynamic characteristics such as excessive gain in the suspension's torsion and sway modes under excitation forces such as air flow and actuator seek motion.